Microelectronic heat treatment methods that make possible production of various layers (for example, of silicon oxide) or the surface treatment of substrates address increasingly severe uniformity parameters.
In fact, the evolution of microelectronics implies reducing the characteristic dimensions of components with the aim of improving both the integration density and the speed of the circuits. In parallel with this, the diameter of the silicon and/or SOI wafers is increasing, going from 200 mm to 300 mm and even 450 mm, with the aim of fabricating ever more dies per wafer. The requirement is therefore to obtain ever finer layers, of ever more controlled and uniform thickness over ever larger areas.
Heat treatment methods are thus confronted with the non-uniform nature of the reactions taking place within the reactor of the unit. This lack of uniformity can have a number of causes:                the intrinsic non-uniformity of the equipment, linked, for example, to the non-uniform power of the heating zones, to the intrinsic accuracy of the temperature sensors, to the shape of the reactor, to the variable gas flows, etc.        the variation of the kinetics of the reaction expected in the reactor through the dilution effect (i.e., impoverishment of the reagent(s)), or the inhibiting effect (i.e., the increasing concentration of the reaction residues).        
The heat treatment units usually employed in the microelectronics industry consist of reactors of large size able to contain a large quantity of substrates (commonly up to 200 substrates). Because of their dimensions, this type of unit includes a plurality of heating elements disposed regularly along the reactor. The heating elements define a plurality of heating zones.
The temperature set points applied to each of the heating zones of a heat treatment unit define a process that aims to establish a target substrate characteristic. This target substrate characteristic may be a particular layer thickness (for example, of an oxide layer) or a surface roughness value below a particular threshold.
For the methods that are the most demanding in terms of the substrate characteristic, it is common to apply set point corrections in each of the heating zones during the initial optimization of the method or between two implementations of the method if “drift” in the characteristic is observed. This correction step is generally referred to as “calibration.”
One calibration method typically used is based on an empirical relation globally linking the temperature and the substrate characteristic in question. Accordingly, when the substrate characteristic is a thickness of an oxide layer generated during the heat treatment, it is established empirically that, for a given method, a particular temperature difference ΔT, with respect to the nominal temperature, generates an oxide thickness difference ΔX. If drift in the substrate characteristic is observed after the execution of a process, the operator applies approximate corrections to the temperature set points of all the heating zones, based on this global relation, so as to compensate for that drift. This purely manual method depends on the assessment by the operator responsible for the calibration of the unit: depending on the ΔX measured on the wafers treated in different positions of the furnace, the correction value ΔT applied can vary depending on the experience of the operator. Recent demanding microelectronics processes cannot tolerate a level of approximation as to the result obtained because the yield of the operation is greatly impacted by the variance in the corrections implemented by the operator.
Moreover, such a correction process does not function perfectly. In fact, it does not take account of the fact that the heating zones are not independent of one another. Applying a ΔT1 to a first heating zone can impact one or more heating zones i of the unit. The greater the set point corrections, the more the mutual influence of the heating zones will interfere with the final result by generating a significant difference versus the result expected by the operator following their temperature set point corrections.
The present disclosure aims to remedy the various drawbacks of the prior art described above.
One object of the present disclosure is to provide a reliable method of calibrating a process employed in a heat treatment unit.
Another object of the present disclosure is to provide an automated calibration method in order to render it more industrial and compatible with high-volume production requirements.